Linagliptin, also called 8-[(3R)-3-Amino-1-piperidinyl]-7-(2-butyn-1-yl)-3,7-dihydro-3-methyl-1-[(4-methyl-2-quinazolinyl)methyl]-1H-purine-2,6-dione, acts as a dipeptidyl peptidase IV inhibitor and is intended to be used for the once-daily oral treatment of type 2 diabetes. In the third quarter 2010, regulatory filings were submitted in the USA, EU and Japan for the approval of Linagliptin for the treatment of diabetes and in the 3rd quarter 2011 Linagliptin received FDA approval.
The chemical structure of Linagliptin is represented by the following formula I

EP1532149 B1 discloses the compound Linagliptin per se and physiologically acceptable salts with inorganic or organic acids thereof.
WO2007/128721 A1 describes crystalline forms A, B, C, D and E of Linagliptin free base. WO2010/072776 A1 describes crystalline acid addition salts of Linagliptin such as the benzoate. In said patent application Linagliptin benzoate is characterized by an X-ray powder diffractogram and a melting point of about 155° C. measured by DSC at defined conditions. Polymorphism is a phenomenon relating to the occurrence of different crystal forms for one molecule. There may be several different crystalline forms for the same molecule with distinct crystal structures and varying in physical properties like melting point, XRPD spectrum and IR-spectrum. These polymorphs are thus distinct solid forms which share the molecular formula of the compound from which the crystals are made up, however they may have distinct advantageous physical properties which can have a direct effect on the ability to process and/or manufacture the drug substance, like flowability, and the drug product, like flowability, as well as on drug product stability, dissolution, and bioavailability.
These distinct physical properties of different polymorphs of the same compound can render different polymorphs more, or less, useful for a particular purpose, such as for pharmaceutical formulation.
The present inventors have discovered that the crystalline form of Linagliptin benzoate of WO2010/072776 A1 is quite hygroscopic. Hygroscopic compounds, however, are difficult to handle under common pharmaceutical processing conditions, such as wet granulation, and they ask for special techniques and equipment in order to avoid e.g. chemical degradation or polymorphic transformation during processing. Furthermore, hygroscopic compounds—and the pharmaceutical compositions containing them—must often be packaged into special containments in order to ensure proper product quality during storage.
Crystal forms of Linagliptin benzoate with better processability for favored formulation conditions, like wet granulation, would facilitate the production of pharmaceutical compositions comprising Linagliptin. There is thus a need for solid forms of Linagliptin which avoid one or more problems of the known Linagliptin benzoate form I.